Application of ASTEC Computer Code for Validation of SAMG Based on LB LOCA Scenario for VVER 1000 – P. Groudev, A. Stefanova, R. Gencheva

In case of unsuccessful application of VVER1000 Emergency Operating Procedures (EOPs) for different reasons during the accident in Nuclear Power Plant (NPP), the operators have to leave the EOPs and to start applying Severe Accident Management Guidance (SAMGs). This paper presents calculation results using computer code for validation of operator actions during severe accident conditions in NPP with VVER-1000 type of reactors. The Kozloduy NPP Units 5&6 has been selected as a reference NPP. As an analytical tool has been used ASTECvp2r3p2 computer code developed by IRSN and GRS.

The work is oriented on investigation of plant behavior mainly after beginning of reactor core heat up, due to simulation of Large Break Loss of Coolant Accident (LB LOCA) with simultaneous loss of AC and DC power. It is assumed that DGs are missing until a certain plant state, and after that they are available.

It have been done calculations without and with operator actions selected based on severe accident management strategies considered in Kozloduy Nuclear Power Plant (KNPP). Based on the SAMG strategies the operator should depressurize primary circuit by gas removing system (YR) if there is a need of additional primary depressurization and to start to cool down the reactor core at 923 K and 1253 K core exit temperatures as it is pointed in SAMG strategy.

The purpose of these analyses is to study the reactor core behavior parameters and to estimate the time available for performing actions. The main goal is to analyze the possibility of preserving the reactor core from damage during a severe accident and to assess hydrogen generation as a result of reflooding of the overheated core. LB LOCA scenario has been selected with break sizes ID 300 mm in the cold leg between main coolant pump (MCP) and reactor pressure vessel. The cold water is injected by a high pressure pump (HPP) in the undamaged cold leg.

Keywords: severe accident, VVER1000, SAMG, ASTEC.